Synthesis and characterization of g-C₃N₄/Ag₂CO₃ with enhanced visible-light photocatalytic activity for the degradation of organic pollutants

Abstract

A facile, simple method was developed for the synthesis of g-C₃N₄/Ag₂CO₃ at room temperature. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and Fourier transformed infrared (FT-IR) spectroscopy. The photocatalytic activity of g-C₃N₄/Ag₂CO₃ composites for the photo-degradation of methyl orange (MO) was much higher than that of the pure Ag₂CO₃. The kinetics of the g-C₃N₄/Ag₂CO₃ composites were proposed. The electrochemical impedance spectroscopy of g-C₃N₄/Ag₂CO₃ composites and a series of radical trapping experiment were also carried out to explore the possible photocatalytic mechanism. The results indicated that the enhanced photocatalytic activity of g-C₃N₄/Ag₂CO₃ composites under visible light irradiation was attributed to the formed heterostructure between g-C₃N₄ and Ag₂CO₃, which was beneficial to the separation of the photoinduced electron–hole pairs.

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1. Introduction

Using catalysts and solar energy in the production of clean energy and the elimination of toxic chemicals, semiconductor photocatalysis has become a most promising technology in the past few years.^1–3 Photocatalytic activity of the materials depends on the efficient separation of the photogenerated electrons and holes. While, the critical points for a good semiconductor photocatalysis are the high efficiency separation of photoexcited electron–hole pairs, the decrease of electron–hole recombination and good repeatability of photocatalysts. Therefore, a significantly efficient, stable, inexpensive, easily separable semiconductor material that work well with visible light is a major challenge in this field.^4,5

Up to now, Ag-based photocatalysts have been identified to be efficient photocatalytic materials under visible light irradiation for the photodegradation of organic pollutants and water splitting for environmentally clean energy in recent years,^6–10 such as Ag₃PO₄,^11,12 Ag₂O,¹³ AgSbO₃.¹⁴ More recently, Ag₂CO₃ semiconductor has been reported that it shows high-efficient degradation ability for dyes under visible light.^15,16 Unfortunately, owing to the photocorrosion,^15,17 Ag₂CO₃ semiconductor also exhibits poor stability. The TiO₂, graphene oxide (GO) and the other materials have been used to improve the photocatalytic activity or the stability of the bulk Ag₂CO₃, such as Ag₂CO₃/TiO₂ (ref. 18) and GO/Ag₂CO₃,^19,20 which exhibit better photocatalytic ability and stability than the bare Ag₂CO₃. In the precious work, Ag₂CO₃ particles semiconductor hindered its performance in photocatalytic processes for large scale applications. Therefore, the critical task is the synthesis of stable nano-sized Ag₂CO₃ particles or the composites.

Recently, graphitic carbon nitride (g-C₃N₄) has been reported as a metal-free semiconductor that has excellent photocatalytic activity for water splitting and the photo-degradation of organic pollutants under visible light irradiation.^4,21,22 g-C₃N₄ has the characteristics of high thermal and chemical stability, versatile optical, electronic, tribological and versatile catalytic properties.^23,24 However, the performance of g-C₃N₄ materials is limited by its drawbacks, which are the high photogenerated electron–hole recombination rate, lower specific surface area and low quantum efficiency.^23,25,26 Therefore, many attempts have been carried out to improve the photocatalytic performance of g-C₃N₄ materials, such as designing nano-/porous structures,^27,28 doping with noble metal or nonmetal elements,^29–31 coupling with other semiconductor materials^23,32–34 etc. Especially, many bulk semiconductors modified with a few mass g-C₃N₄ can increase the photocatalytic activity for the degradation of organic pollutants, such as g-C₃N₄/ZnO,³⁵ g-C₃N₄/TiO₂ (ref. 36) and g-C₃N₄/Cu₂O.³⁷ The enhanced photocatalytic activity is attributed to the heterostructures between g-C₃N₄ with the bulk semiconductors. This method provide a feasible route to promote the separation efficiency of photogenerated electron–holes pairs and extend the light response of the photocatalyst. Based on the precious work, the photocatalytic performance may be enhanced if g-C₃N₄ is introduced into Ag₂CO₃ material. Besides, there are few works focusing on the preparation and photocatalytic properties of g-C₃N₄/Ag₂CO₃ composite materials.

In this work, a facile precipitation reaction was reported for the synthesis of Ag₂CO₃/g-C₃N₄ photocatalyst at room temperature. The g-C₃N₄/Ag₂CO₃ composites were characterized by X-ray powder diffraction (XRD), X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and ultraviolet visible diffuse reflectance spectroscopy (DRS). The as-obtained products were used as photocatalysts for the degradation of methyl orange (MO) under visible light irradiation. In particular, the effect of g-C₃N₄ content in composites has been investigated on the photocatalytic degradation efficiency. Besides, the possible photocatalytic mechanism was proposed based on the present experimental results.

2. Experimental

2.1 Preparation of the g-C₃N₄/Ag₂CO₃ photocatalysts

2.1.1 Preparation of graphitic carbon nitride. Graphitic carbon nitride (g-C₃N₄) was synthesized by a hydrothermal method. In a typical procedure, 2.5 mmol melamine powders and 5 mmol 1.3.5-trichlorotriazine were respectively poured into a 25 mL Teflon-lined antoclave, and then organic solvent was added into the Teflon-lined antoclave up to 80% of the total volume. The mixture was stirred for 12 h. Then the autoclave was heated at 160 °C for 48 h and cooled down to room temperature. In order to remove residual impurities, the obtained product was sequentially washed with absolute ethanol and distilled water several times, and then the resulting powder was dried at 50 °C for 24 h to obtain the final product.³⁸

2.1.2 Synthesis of Ag₂CO₃. The Ag₂CO₃ samples were prepared by a typical synthesis: AgNO₃ (0.680 g) was completely placed in a beaker at room temperature. Then, 0.5 mL NH₃·H₂O solution (0.2 M) was added dropwise to the beaker under magnetic stirring. 10 min later, the aqueous solution of NaHCO₃ (20 mL, 0.2 M) was added dropwise to the beaker and then the color of the solution immediately changed yellow. The mixture was stirred for 10 min and 0.25 mL HNO₃ (0.2 M) was dropwise in the beaker and then the products was obtained after continuous stirring 60 min. The products were collected by centrifugation and washed several times with distilled water and ethyl alcohol, and then dried at 35 °C for 6 h.

2.1.3 Synthesis of the g-C₃N₄/Ag₂CO₃ composites. Firstly, g-C₃N₄ (0.017 g) was completely dispersed in distilled water by ultrasound for 30 min. Secondly, AgNO₃ (0.679 g) was added to the above g-C₃N₄ aqueous suspension and sonicated for 15 min. Then, 0.5 mL NH₃·H₂O solution (0.2 M) was added dropwise to the beaker under magnetic stirring for 10 min. Then, NaHCO₃ aqueous solution (20 mL, 0.2 M) was added dropwise to the mixture. The mixture was stirred for 10 min and 0.25 mL HNO₃(0.2 M) was dropwise in the beaker and then the products was obtained after continuous stirring 60 min. Lastly, the products were collected by centrifugation and washed several times with distilled water and ethyl alcohol, and then dried at 35 °C for 6 h. Other substances containing different weight proportions of g-C₃N₄ (1 wt%, 7 wt%) could also be obtained with the same method.

2.2 Characterization of the g-C₃N₄/Ag₂CO₃

X-Ray powder diffraction (XRD) was obtained on a Bruker D8 diffractometer using Cu-Kα radiation (λ = 1.5418 Å) in the range of 2θ = 10–80°. X-ray photoemission spectroscopy (XPS) measurements were performed on a VG MultiLab 2000 system with a monochromatic Mg-Kα source operated at 20 kV. Transmission electron microscopy (TEM) were taken with a JEOL-JEM-010 (JELO, Japan) operated at 200 kV. Ultraviolet visible (UV-vis) diffuse reflection spectra were measured using a UV-vis spectrophotometer (Shimadzu UV-2450, Japan) in the range 200–800 nm. BaSO₄ was used as the reflectance standard material. Fourier transform infrared (FT-IR) spectra of all the catalysts (KBr pellets) were recorded in KBr pellets with Nicolet Model Nexus 470 FT-IR equipment.

2.3 Photocatalytic activity measurement

The photocatalytic activity of the products was compared by measuring the photodegradation of MO under 300 W Xe lamp with a 400 nm cutoff filter. In a typical measurement, 0.040 g photocatalyst was added into 60 mL MO (10 mg L⁻¹) in a Pyrex photocatalytic reactor. Prior to irradiation, the suspensions were magnetically stirred for 60 min in the dark to reach the absorption–desorption equilibrium on the photocatalyst surface. Furthermore, all the experiments were performed at 30 °C under constant stirring. At irradiation time intervals of 20 min, 3 mL solution was collected and centrifuged to remove the photocatalyst particles at a certain time intervals. Then, the filtrates were analyzed by using a Shimadzu UV-2450 spectrophotometer to record the maximum absorption band (MO: 463 nm).

3. Results and discussion

3.1 Synthesis process of the g-C₃N₄/Ag₂CO₃ composites

The process for the synthesis of the g-C₃N₄/Ag₂CO₃ composites is shown in Fig. 1. Silver salt is mixed with an ultrasonically dispersed g-C₃N₄ sheet and the Ag⁺ is bound to the surface of the g-C₃N₄ attributing to its chemical absorbing. Then, Ag(NH₃)₂⁺ is formed after the adding of NH₃·H₂O. The ion-exchanged reactions between Ag(NH₃)₂⁺ and CO₃²⁻ on the surface of the g-C₃N₄ sheet occurred and led to the formation of g-C₃N₄/Ag₂CO₃ after the addition of NaHCO₃ under the constant stirring at the room temperature. Besides, Ag₂CO₃ particles were deposited on the surface of g-C₃N₄ sheet and the heterojunction structure between g-C₃N₄ and Ag₂CO₃ could be formed.

Fig. 1 Schematic representation for the synthesis of g-C₃N₄/Ag₂CO₃ composite.

3.2 XRD analysis

The crystal structure of the g-C₃N₄/Ag₂CO₃ composites was characterized by XRD. The XRD patterns of g-C₃N₄, Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ composites are shown in Fig. 2. The results indicate that the strong diffraction peak at 27.4° which appears in the bulk g-C₃N₄ and g-C₃N₄/Ag₂CO₃ composites is corresponding to the (002) plane of g-C₃N₄.^23,38,39 The Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ composites have similar peaks. Besides, their diffraction peaks (from 15° to 55°) are indexed to (100), (110), (−101), (130), (200), (031), (220), (131), (230) and (221) planes of the monoclinic crystal structure (JCPDS card no. 26-0339). With the increasing amount of g-C₃N₄, the peak intention of Ag₂CO₃ in the g-C₃N₄/Ag₂CO₃ composites decrease and the peak of g-C₃N₄ in the g-C₃N₄/Ag₂CO₃ composites appears. In order to identify the existence of g-C₃N₄ in the g-C₃N₄/Ag₂CO₃ composites, the samples were also analyzed by the other TEM and FT-IR analyses.

Fig. 2 XRD patterns of Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ samples.

3.3 XPS analysis

The XPS were carried out to analyze the oxidation state and the surface chemical composition of the samples. Fig. 3(a) shows the C, N, O and Ag elements in the g-C₃N₄/Ag₂CO₃ composites, indicating that the preparation process does not bring any impurities. Two peaks located at 374.0 eV and 368.0 eV are assigned the Ag 3d_3/2 and Ag 3d_5/2, indicating the existence of Ag⁺ (Fig.3(b)).^20,25,40 The C 1s XPS spectra was shown in Fig. 3(c). High-resolution spectra of C1s at 287.4 eV assigned to the sp² C=N bond in the s-triazine ring.⁴¹ The C peaks at 284.8 was identified as the typical sp² C–C bonds of CN.⁴² The C peak at 288.5 eV could be assigned to the overlapped peak of the sp²-hybridized carbon in the trizine rings (N–C=N) and the carbonate ion in Ag₂CO₃ sample.⁴³ Fig. 3(d) showed the O 1s XPS spectra of the samples. The O1s peak at 530.8 eV was attributed to the O element of silver carbonate.^17,40 The XPS spectra of N 1s was shown in Fig. 3(e). The main peaks at around 398.2 eV and 399.6 eV were ascribed to sp² hybridized aromatic N bonded to carbon atoms in the form of C=N–C and the tertiary N bonded to carbon atoms (N–(C)₃).^41,44 The peak at 400.2 eV could be assigned to C–N–H.⁴⁵ Based on the above analysis, the g-C₃N₄ existed in the g-C₃N₄/Ag₂CO₃ composites.

Fig. 3 XPS spectra of (a) g-C₃N₄/Ag₂CO₃ (b) Ag 3d (c) C 1s (d) O 1s (e) N 1s.

3.4 TEM analysis

The morphology of the g-C₃N₄/Ag₂CO₃ composites were also investigated by TEM. Fig. 4(a and b) shows the TEM images of the Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ samples. Fig. 4(a) shows that there is no distinctive morphological features appearing for the Ag₂CO₃ particles. Fig. 4(b) shows the Ag₂CO₃ particles are wrapped by g-C₃N₄. From the TEM images of Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ samples, it can be seen that g-C₃N₄ was successfully dispersed on the surface of Ag₂CO₃ and the heterostructure between g-C₃N₄ and Ag₂CO₃ was formed in the g-C₃N₄/Ag₂CO₃ composites. The SAED pattern taken from the edge of the microsphere is shown in Fig. 4(c). It could be seen that the Ag₂CO₃ sample almost exhibits a polycrystalline diffraction pattern.

Fig. 4 TEM images of (a) Ag₂CO₃, (b) g-C₃N₄/Ag₂CO₃ (3 wt%), (c) the SEAD pattern of Ag₂CO₃.

3.5 DRS analysis

UV-vis diffuse reflectance spectroscopy was carried out to investigate the optical properties of the samples. The results are shown in Fig. 5. The band gap absorption edge of pure g-C₃N₄ is around 650 nm. The fundamental band gap absorption edge of the pure Ag₂CO₃ is around 470 nm.²⁰ As shown in Fig. 5, the g-C₃N₄/Ag₂CO₃ composites exhibited a mixed absorption property of g-C₃N₄ and Ag₂CO₃. Moreover, the absorption intention of the g-C₃N₄/Ag₂CO₃ composites increase greatly with the increasing amount of g-C₃N₄ in the visible light region. Besides, the absorption edge of the g-C₃N₄/Ag₂CO₃ composites have a little red shift compared with that of the pure Ag₂CO₃. Obviously, the introduction of g-C₃N₄ significantly enhanced the absorption in the visible light region of the g-C₃N₄/Ag₂CO₃ composites.

Fig. 5 UV-vis diffuse reflectance spectra of the samples.

3.6 FT-IR analysis

The FT-IR spectra of g-C₃N₄, pure Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ composites are shown in Fig. 6. In the FT-IR spectra of g-C₃N₄, the broad band at 3000–3300 cm⁻¹ is due to the stretching modes of terminal NH₂ or NH groups at the defect sites of the aromatic ring.^38,46 The observed peaks at 1300–1700 cm⁻¹ are attributed to stretching modes of C–N heterocycles.^38,46 The peak at 800 cm⁻¹ is related to the characteristic breathing mode of triazine units.^25,38,46 In the FT-IR spectra of the pure Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ composites, the characteristic absorption bands of CO₃²⁻ could be observed at 708 cm⁻¹, 802 cm⁻¹, 883 cm⁻¹, 1328 cm⁻¹ and 1449 cm⁻¹.²⁰ Besides, the peaks at 1640 cm⁻¹ and 1540 cm⁻¹ are found and the peak intention of CO₃²⁻ decreased in the FT-IR spectra of the g-C₃N₄/Ag₂CO₃ (7 wt%) composite. It can be explained by the following reason: the chemical environment of bare Ag₂CO₃ was changed by the existence of g-C₃N₄.

Fig. 6 FT-IR spectra of g-C₃N₄, Ag₂CO₃ and g-C₃N₄/Ag₂CO₃.

3.7 Photocatalytic activity

The photocatalytic activity of the pure Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ composites were evaluated via the photodegradation of MO under visible light irradiation (as shown in Fig. 7(a)). Obviously, all the g-C₃N₄/Ag₂CO₃ composites show better photodegradation performance than the pure Ag₂CO₃ and g-C₃N₄. With the increasing g-C₃N₄ content, the photocatalytic activity first increases and then decreases. Furthermore, the g-C₃N₄/Ag₂CO₃ (3 wt%) composite excites the highest photocatalytic activities for the photodegradation of MO, indicating that the amount of g-C₃N₄ affects photocatalytic activity of the composite. However, when g-C₃N₄ content increases above 3 wt%, the photocatalytic efficiency decreases, although it remains higher than that of pure Ag₂CO₃. More g-C₃N₄ may reduce the electron transfer efficiency of the photoinduced electrons from Ag₂CO₃ nanoparticles to g-C₃N₄ surfaces, so the activity decreased under visible light irradiation.⁴ Fig. 7(b) shows the temporal evolution of the spectral changes of MO solution (10 mg L⁻¹) mediated by Ag₂CO₃ under visible light irradiation. Fig. 7(c) shows the temporal evolution of the spectral changes of MO solution (10 mg L⁻¹) mediated by g-C₃N₄/Ag₂CO₃ (3 wt%) under visible light irradiation. The absorption peak of MO located at 463 nm decreases rapidly with increasing degradation time, and the MO dye is almost completely degraded after 2 h.

Fig. 7 (a) The photocatalytic degradation of MO by the samples, (b and c) absorption spectral changes of MO under visible light irradiation (pure Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ (3 wt%)).

3.8 Kinetics

To investigate the kinetics of MO photocatalytic degradation by the pure Ag₂CO₃ and the g-C₃N₄/Ag₂CO₃ composites, the experimental data were fitted by applying a first order model with a simplified Langmuir–Hinshelwood model⁴⁷ as expressed by below equation: ln(C_t/C₀) = −kt, where k is the apparent reaction rate constant, C₀ is the adsorption equilibrium concentration of MO, t is the reaction time, and C is the concentration of MO at the reaction time t. As shown in Fig. 8, it can be seen that the photodegradation rate of all the samples is higher than that of the pure Ag₂CO₃ under visible light irradiation. With the increasing content of g-C₃N₄, the photodegradation rate first increased and then decreased. Apparently, the photodegradation rate constant k of g-C₃N₄/Ag₂CO₃ composite (3 wt%) was 2.5187 min⁻¹, which was 9.2 times higher than that of the pure Ag₂CO₃. These results indicated that the introduction of g-C₃N₄ enhanced the photoinduced electron–holes separation and thus improved the photocatalytic activities of the samples.

Fig. 8 Photocatalytic degradation kinetics of MO by g-C₃N₄/Ag₂CO₃ composites under visible light irradiation.

3.9 Electrochemical impedance spectroscopy

To further investigate charge transfer and recombination processes in the g-C₃N₄/Ag₂CO₃ composites, electrochemical impedance spectroscopy (EIS) Nyquist plots of the pure Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ (3 wt%) composites has been carried out under the visible light irradiation. As shown in Fig. 9, the smaller arc radius on the EIS Nyquist plot of g-C₃N₄/Ag₂CO₃ (3 wt%) could be observed under the visible light irradiation, indicating that a more effective separation of photogenerated electron–hole pairs and a faster interfacial charge transfer had occurred on the surface of g-C₃N₄/Ag₂CO₃ (3 wt%) composite.

Fig. 9 Electrochemical impedance spectroscopy of the pure Ag₂CO₃ and g-C₃N₄/Ag₂CO₃ (3 wt%) in 1 M Na₂SO₄ aqueous solution under visible light irradiation.

3.10 Possible photocatalytic mechanisms

It is well-known that the key factors to enhance photocatalytic activity are an efficient charge separation and high adsorption. According to the recent reports, g-C₃N₄ has been proved to be an effective electron transporter and acceptor in the systems of g-C₃N₄/TiO₂, g-C₃N₄/Ag₃PO₄ and g-C₃N₄/CdS. The g-C₃N₄ sheets could promote charge migration and decrease the recombination of electron–hole pairs of the g-C₃N₄ based photocatalysts.^48,49 Therefore, the reinforced charge migration may be achieved in the g-C₃N₄/Ag₂CO₃ composites.

The experiments of in situ capture of active pieces were conducted to further investigate the photocatalytic mechanism. In that experiment, EDTA-2Na (ref. 50) served as the holes scavenge and t-BuOH served as the hydroxyl radical scavenger.⁵¹ In Fig. 10, the photo-degradation efficiency of MO over g-C₃N₄/Ag₂CO₃ (3 wt%) composite was completely inhibited by the holes scavenge, while the photo-degradation efficiency of MO over g-C₃N₄/Ag₂CO₃ (3 wt%) composite slightly decreased by the hydroxyl radical scavenger. The results indicated that the radical holes were the main oxidative species in the photocatalytic reaction system.

Fig. 10 Plots of photogenerated active species trapped in the system of photodegradation of MO by g-C₃N₄/Ag₂CO₃ (3 wt%) under visible light irradiation.

To evaluate the stability and reusability of the g-C₃N₄/Ag₂CO₃ hybrid photocatalyst, it carried out the additional experiments to degrade MO under visible light cycled for three times. It could be found that the photocatalytic activity of g-C₃N₄/Ag₂CO₃ (3 wt%) for MO degradation decreased from 92% to 50% after three cycling runs. The XRD analysis of the samples (three cycling runs) indicated that the intensity of recycled g-C₃N₄/Ag₂CO₃ (3 wt%) sample decreased and the diffraction peak at 2θ values 38.1° was assigned to the (111) lattice plane of Ag nanoparticles (Fig. 11).^52–54 So during the photocatalytic reaction, the g-C₃N₄/Ag₂CO₃ system was transformed to be g-C₃N₄/Ag/Ag₂CO₃ system. There are two reason to explain the decreasing photocatalytic activity of the g-C₃N₄/Ag₂CO₃ composites after three cycling runs. For one thing, the Ag nanoparticles gradually grew on the Ag₂CO₃ surface under the photocatalytic reaction process, which could prevent the light absorption of Ag₂CO₃. For the other thing, the formed Ag⁰ also become the capture center of the electron and hole.

Fig. 11 (A) The XRD patterns of used g-C₃N₄/Ag₂CO₃ (3 wt%) sample, (B) the XRD pattern at 2θ = 35°–40°.

Based on the above analyses and the related literature reports, the schematic mechanism of the enhanced photocatalytic activity of the g-C₃N₄/Ag₂CO₃ composites was proposed and shown in Fig. 12. Under visible light irradiation, both g-C₃N₄ and Ag₂CO₃ could absorb visible light and were all excited to generate electron and hole pairs. The photoinduced holes on the valence band of Ag₂CO₃ could move quickly to g-C₃N₄ because the valence band potential of g-C₃N₄ (+1.765 V) was more negative than that of Ag₂CO₃ (+2.673 V). The holes on the surface of g-C₃N₄ could directly decompose the MO molecules into the intermediates. Meanwhile, the photogenerated electrons of g-C₃N₄ in the composites could easily transfer to the surface of Ag₂CO₃. The accumulated electrons would reduce parts of Ag⁺ to form metal Ag nanoparticles on the surface of Ag₂CO₃. The matching band potentials between Ag₂CO₃ and g-C₃N₄ could effectively suppress the electron–hole recombination and promote the separation efficiency, which greatly promoted the photocatalytic degradation of MO. The similar phenomenon appeared in Ag@AgBr/g-C₃N₄,⁵⁴ Ag₃VO₄/AgBr/Ag.⁵⁵

Fig. 12 Photocatalytic mechanism diagram of the g-C₃N₄/Ag₂CO₃ samples.

4. Conclusions

In summary, the novel g-C₃N₄/Ag₂CO₃ composites were synthesized by using a facile, simple method. The obtained g-C₃N₄/Ag₂CO₃ composites exhibited much enhanced photocatalytic activity in the degradation of MO in comparing with the pure Ag₂CO₃ under visible light irradiation. The remarkable catalysis enhancement can be attributed to the effective separation of photogenerated electrons–hole pairs, which was due to the formed heterostructure between the two semiconductors. Besides, with increasing the amount of g-C₃N₄, the photocatalytic ability increased in a suitable range. Consequently, our work can provide a facile, simple, effective method to synthesis other visible light active photocatalysts for environmental applications as well as water splitting.

Acknowledgements

The authors genuinely appreciate the financial support of this work from the National Nature Science Foundation of China (no. 21177050, 21206060 and 21376109), Natural Science Foundation of Jiangsu Province (BK20131207, BK20140533), Postdoctoral Foundation of China (2014M551520, 2013M541619), Doctoral Innovation Fund of Jiangsu Province (CXLX13-651) and Opening Project (no. SJHG1308) of the Jiangsu Key Laboratory for Environment Functional Materials.

References

1. S. Kumar, T. Surendar, B. Kumar, A. Baruah and V. Shanker, J. Phys. Chem. C, 2013, 117, 26135–26143.
2. X. B. Chen, S. H. Shen, L. J. Guo and S. S. Mao, Chem. Rev., 2010, 110, 6503–6570.
3. F. J. Zhang, F. Z. Xie, S. F. Zhu, J. Liu, J. Zhang, S. F. Mei and W. Zhao, Chem. Eng. News, 2013, 228, 435–441.
4. S. Kumar, T. Surendar, B. Kumar, A. Baruah and V. Shanker, J. Mater. Chem. A, 2013, 1, 5333–5340.
5. J. Fu, B. B. Chang, Y. L. Tian, F. N. Xi and X. P. Dong, J. Mater. Chem. A, 2013, 1, 3083–3090.
6. Z. Y. Ji, X. P. Shen, J. L. Yang, Y. L. Xu, G. X. Zhu and K. M. Chen, Eur. J. Inorg. Chem., 2013, 36, 6119–6125.
7. P. Wang, B. B. Huang, Y. Dai and M. H. Whangbo, Phys. Chem. Chem. Phys., 2012, 14, 9813–9825.
8. H. F. Cheng, B. B. Huang, P. Wang, Z. Y. Wang, Z. Z. Lou, J. P. Wang, X. Y. Qin, X. Y. Zhang and Y. Dai, Chem. Commun., 2011, 47, 7054–7056.
9. J. X. Sun, Y. P. Yua, L. G. Qiu, X. Jiang, A. J. Xie, Y. H. Shen and J. F. Zhu, Dalton Trans., 2012, 41, 6756–6763.
10. W. F. Yao, B. Zhang, C. P. Huang, C. Ma, X. L. Song and Q. J. Xu, J. Mater. Chem., 2012, 22, 4050–4055.
11. V. Shanker and T. Surendar, Mater. Lett., 2014, 123, 172–175.
12. J. H. Liu, X. Li, F. Liu, L. H. Lu, L. Xu, L. W. Liu, W. Chen, L. M. Duan and Z. R. Liu, Catal. Commun., 2014, 46, 138–141.
13. Y. J. Jin, Z. Y. Dai, F. Liu, H. J. Kim, M. P. Tong and Y. L. Hou, Water Res., 2013, 47, 1837–1847.
14. W. J. Liu, X. B. Liu, Y. H. Fu, Q. Q. You, R. K. Huang, P. Liu and Z. H. Li, Appl. Catal., B, 2012, 123–124, 78–83.
15. G. P. Dai, J. G. Yu and G. Liu, J. Phys. Chem. C, 2012, 116, 15519–15524.
16. H. J. Dong, G. Chen, J. X. Sun, C. M. Li, Y. G. Yu and D. H. Chen, Appl. Catal., B, 2013, 134–135, 46–54.
17. C. L. Yu, G. Li, S. Kumar, K. Yang and R. C. Jin, Adv. Mater., 2014, 26, 892–898.
18. Y. Wang, P. H. Ren, C. X. Feng, X. Zheng, Z. G. Wang and D. L. Li, Mater. Lett., 2014, 115, 85–88.
19. C. Dong, K. L. Wu, X. W. Wei, X. Z. Li, L. Liu, T. H. Ding, J. Wang and Y. Ye, Cryst. Eng. Commun., 2014, 16, 730–736.
20. Y. X. Song, J. X. Zhu, H. Xu, C. Wang, Y. G. Xu, H. Y. Ji, K. Wang, Q. Zhang and H. M. Li, J. Alloys Compd., 2014, 592, 258–265.
21. X. C. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen and M. Antonietti, Nat. Mater., 2009, 8, 76.
22. J. Di, J. X. Xia, S. Yin, H. Xu, L. Xu, Y. G. Xu, M. Q. He and H. M. Li, J. Mater. Chem. A, 2014, 2, 5340–5351.
23. Y. M. He, J. Cai, T. T. Li, Y. Wu, Y. M. Yi, M. F. Luo and L. H. Zhao, Ind. Eng. Chem. Res., 2012, 51, 14729–14737.
24. C. Liu, L. Q. Jing, L. M. He, Y. B. Luan and C. M. Li, Chem. Commun., 2014, 50, 1999–2001.
25. H. Xu, J. Yan, Y. G. Xu, Y. H. Song, H. M. Li, J. X. Xia, C. J. Huang and H. L. Wan, Appl. Catal., B, 2013, 129, 182–193.
26. S. W. Zhang, J. X. Li, M. Y. Zeng, G. X. Zhao, J. Z. Xu, W. P. Hu and X. K. Wang, ACS Appl. Mater. Interfaces., 2013, 5, 12735–12743.
27. X. C. Wang, K. Maeda, X. F. Chen, K. Takanabe, K. Domen, Y. D. Hou, X. Z. Fu and M. Antonietti, J. Am. Chem. Soc., 2009, 131, 1680–1681.
28. H. J. Yan, Chem. Commun., 2012, 48, 3430–3432.
29. X. C. Wang, X. F. Chen, A. Thomas, X. Z. Fu and M. Antonietti, Adv. Mater., 2009, 21, 1609–1612.
30. S. C. Yan, Z. S. Li and Z. G. Zou, Langmuir, 2010, 26, 3894–3901.
31. G. Liu, P. Niu, C. H. Sun, S. C. Smith, Z. G. Chen, G. Q. Lu and H. M. Cheng, J. Am. Chem. Soc., 2010, 132, 11642–11648.
32. S. C. Yan, S. B. Lv, Z. S. Li and Z. G. Zou, Dalton Trans., 2010, 39, 1488–1491.
33. Y. J. Zhang, T. Mori, L. Niu and J. H. Ye, Energy Environ. Sci., 2011, 4, 4517–4521.
34. T. P. Ang and Y. M. Chan, J. Phys. Chem. C, 2011, 115, 15965–15972.
35. X. F. Li, M. Li, J. H. Yang, X. Y. Li, T. J. Hu, J. S. Wang, Y. R. Sui, X. T. Wu and L. N. Kong, J. Phys. Chem. Sol., 2014, 75, 441–446.
36. C. Miranda, H. Mansilla, J. Yanez, S. Obregon and G. Colon, J. Photochem. Photobiol., A, 2013, 253, 16–21.
37. J. Chen, S. H. Shen, P. H. Guo, M. Wang, P. Wu, X. X. Wang and L. J. Guo, Appl. Catal., B, 2014, 152–153, 335–341.
38. Y. J. Cui, Z. X. Ding, X. Z. Fu and X. C. Wang, Angew. Chem., Int. Ed., 2012, 51, 11814–11818.
39. X. J. Bai, L. Wang, Y. J. Wang, W. Q. Yao and Y. F. Zhu, Appl. Catal., B, 2014, 152–153, 262–270.
40. H. J. Dong, G. Chen, J. X. Sun, C. M. Li, Y. G. Yu and D. H. Chen, Appl. Catal., B, 2013, 134–135, 46–54.
41. J. G. Yu, K. Wang, W. Xiao and B. Cheng, Phys. Chem. Chem. Phys., 2014, 16, 11492–11501.
42. X. J. Wang, W. Y. Yang, F. T. Li, Y. B. Xue, R. H. Liu and Y. J. Hao, Ind. Eng. Chem. Res., 2013, 52, 17140–17150.
43. W. D. Zhang, Y. J. Sun, F. Dong, W. Zhang, S. Duan and Q. Zhang, Dalton Trans., 2014 10.1039/c4dt00513a.
44. L. Q. Ye, J. Y. Liu, Z. Jiang, T. Y. Peng and L. Zan, Appl. Catal., B, 2013, 142–143, 1–7.
45. Z. Y. Zhang, J. D. Huang, Q. Yuan and B. Dong, Nanoscale, 2014, 26, 9250–9256.
46. Z. L. Xiu, H. Bo, Y. Z. Wu and X. P. Hao, Appl. Surf. Sci., 2014, 289, 394–399.
47. C. S. Turchi and D. F. Ollis, J. Catal., 1990, 112, 178–192.
48. S. Kumar, T. Surendar, B. Kumar, A. Baruah and V. Shanker, RSC Adv., 2014, 4, 8132–8137.
49. H. X. Zhao, H. T. Yu, X. Quan, S. Chen, H. M. Zhao and H. Wang, RSC Adv., 2014, 4, 624–628.
50. S. Feng, H. Xu, L. Liu, Y. H. Song, H. M. Li, Y. G. Xu, J. X. Xia, S. Yin and J. Yan, Colloids Surf. A, 2012, 410, 23–30.
51. M. R. Hoffmanm, S. T. Martin, W. Choi and D. W. Bahnemann, Chem. Rev., 1995, 95, 69–96.
52. C. D. Tamuly, M. Hazarika, M. Bordoloi and M. R. Das, Mater. Lett., 2013, 102–103, 1–4.
53. B. Z. Tian, R. F. Dong, J. M. Zhang, S. Y. Bao, F. Yang and J. L. Zhang, Appl. Catal., B, 2014, 158–159, 76–84.
54. Y. X. Yang, W. Guo, Y. N. Guo, Y. H. Zhao, X. Yuan and Y. H. Guo, J. Hazard. Mater., 2014, 271, 150–159.
55. Q. Zhu, W. S. Wang, L. Lin, G. Q. Gao, H. L. Guo, H. Du and A. W. Xu, J. Phys. Chem. C, 2013, 117, 5894–5900.

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